1. Field of the Invention
The disclosed subject matter relates to methods and systems for removal of gaseous contaminants from gas streams.
2. Description of Related Art
In conventional industrial technologies for gas purification, impurities, such as H2S, CO2 and/or COS are removed from a gas stream such as flue gas, natural gas, syngas or other gas streams by absorption in a liquid wash solution, e.g., in a liquid solution comprising an amine compound.
Used wash solution is subsequently regenerated in a regenerator column (also referred to as a “regenerator”) to release the impurities present in the solution, typically by countercurrent contact with steam. The steam needed for regeneration is typically produced by boiling the regenerated wash solution in a reboiler that is, located near the bottom portion of the regenerator column. In addition, the reboiling of the regenerated wash solution may provide further release of impurities present in the wash solution.
In conventional absorption-regeneration processes as described above, regenerated and reboiled wash solution is typically re-used in another absorption cycle. However, the reboiled solution may have a temperature as high as 100-150° C. To enable efficient absorption, wash solutions based on amine compounds are typically cooled before being passed to another round of absorption. Cooling has conventionally been accomplished by heat-exchange with used wash solution from the absorption process.
The energy produced by the reboiler is not only used for regeneration, but also at other locations in an absorption-regeneration process. In general, the energy requirements of a conventional gas purification process are of three types: binding energy, stripping energy and sensible heat. Binding energy is required for breaking the chemical bond formed between the impurities and the wash solution, whereas stripping energy is required for production of the steam needed for releasing the impurities from the wash solution. Sensible heat is in turn needed for heating of the wash solution prior to regeneration. In conventional systems and processes, part of the produced energy may be lost for example, in the system coolers, which reduce the temperature at specified locations in the system, e.g., the cooler located near the absorber inlet for cooling return wash solution before feeding it to the absorber. Moreover, energy may be lost in condensers located at the top of the absorber, regenerator etc., and in the form of water vapor exiting the process, mostly at the top of the regenerator where water vapor is present in the purified CO2 gas.
Thus, contaminant removal from gas streams, and in particular the regeneration of wash solutions, is an energy intensive process. Reduction of energy requirements at different parts of a gas purification process could potentially reduce the total energy required by the system.